In most primate species, the members of one sex migrate around the time of puberty, leaving their birth group and attempting to join another group in which they then reproduce. Decisions about when, where, and with whom to migrate are possibly the most important decisions that these individuals make, because they have tremendous impact on risk of death, as well as access to breeding opportunities. In white-faced capuchin monkeys (Cebus capucinus), males migrate multiple times, whereas females remain in their birth groups. Males migrate either singly or with allies. Because new immigrants who take over the alpha male position often kill infants, it may be expected that the presence of recent immigrants is a source of stress for females as well as males. This project, a continuation of an 18-year study documenting the life histories of 107 white-faced capuchin monkeys in 11 social groups, will collect demographic and behavioral data, as well as genetic and hormonal data (collected non-invasively from feces) to access the factors that contribute to migration strategies for males, and counter-strategies for females trying to protect their offspring from new immigrants who might kill the infants. Extensive behavioral records will enable testing of hypotheses regarding the effects of relationship quality, play experience and personality on the effectiveness of particular migration tactics. The Lomas Barbudal Monkey Project will provide year-long internships to 18 students, preparing them for graduate school and conservation jobs. The project also provides research opportunities for postdoctoral fellows and graduate students. The PI and the long-term research assistants serve as consultants to the Costa Rican Park Service and local landowners by providing recommendations for reforestation and ways to mitigate the negative effects of development and tourism on wildlife. Project staff members also create educational materials and give presentations on conservation at primary schools near the study site.

Project Report

Wild capuchin monkeys live in social groups in which females remain with their female relatives all their lives, while males migrate to other social groups several times during their lives, sometimes migrating alone and sometimes with other males. Migration is a high risk event, with increased potential for harm and important implications for breeding success. This project documented the social, genetic and physiological factors that influence the success of different male migration strategies, and the effects of male turnover on female physiology and reproductive success for white-faced capuchins at Lomas Barbudal Biological Reserve, Costa Rica. The results indicated that males who migrate together are usually genetically related (at the level of half-sibling, on average), and they are more likely to achieve an alpha male takeover in the new group compared to males who migrate alone. Alpha males have higher levels of testosterone and cortisol than lower ranking males, and male reproductive success is strongly related to achieving and maintaining alpha male status. Alpha male tenure depends on successful alliances with subordinate males to defend against rank challenges and incursions by migrant males from other groups. Early in their tenures, alpha males monopolize breeding, siring 92% of all offspring produced. But if an alpha male succeeds in holding his position for more than six years, his own daughters and granddaughters reach reproductive age and father-daughter inbreeding avoidance prevents the alpha male from breeding with his female descendants; under these circumstances, approximately half of all infants were sired by the alpha male’s subordinate male allies. The greatest contributor to infant mortality is infanticide by immigrant males, and prevention of infanticide is one of the greatest challenges females face in enhancing their lifetime reproductive success. Changes in the identity of the alpha male are a great threat to female reproductive success, which females combat by supporting the current alpha male and forming coalitions against potentially infanticidal male migrants. Cortisol levels for pregnant females and for females who have just given birth are slightly (non-significantly) higher if the females live in groups that have undergone changes in the identity of the alpha male during their pregnancies or around the time of conception. Broader impacts: During the course of this 4-year project, 41 recent college graduates, including 25 women, were given the opportunity to do fieldwork. Ten graduate students (including six women) from various institutions used data collected from this project in their research, and mathematical modelers from multiple institutions are using these data to test their models of various social strategies. Perry and members of her staff gave talks about monkey behavior and tropical dry forest conservation to a wide range of audiences, including K-12 schoolchildren in Costa Rica and the US, community members in Costa Rica, university students in the US, and scientific conferences. Collaborations with film crews from institutions such as the BBC and NHK will result in nature documentaries distributed worldwide. Members of this research group collaborate with the Costa Rican park service to accomplish conservation goals, by aiding in biological monitoring, aiding in vigilance against fires and poaching, and reforesting land damaged by human activities.

National Science Foundation (NSF)
Division of Behavioral and Cognitive Sciences (BCS)
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Carolyn Ehardt
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University of California Los Angeles
Los Angeles
United States
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